Sand and/or gravel mixed with water in the form of a slurry are lifted from the river bottom by means of dredging pumps connected to a suction pipe. The capacity of these pumps range from about 1,000 to 10,000 cubic meters per hour (m.sup.3 /h) of slurry having a volume concentration of solids ranging from about 8 to 20 percent, depending on the character of the soil being dredged. Such a comparatively low grade slurry has great kinetic energy as the speed of its motion through the pipes is 2 or more meters per second in order to avoid the deposition of the transported material, i.e. the clogging of the pipe. In most cases the gravel or the sand is loaded on vessels or barges of varying tonnage, and is transported to an unloading point. The loading of the sand and/or gravel is performed by pouring the slurry into the vessel's hold in which the gravel, as the useful cargo, is deposited, while the water, having served its purpose as the transportation medium, flows back into the river over the rim or through special overflow ports in the vessel's hold.
During the loading or unloading operation when the sand and gravel slurry is carried by means of pipes in accordance with prior art techniques, the following problems arise:
1. Because of the high kinetic energy of the slurry, it cannot be loaded on small capacity vessels or on standard cargo boats. Accordingly, high capacity dredgers can only use large specially built vessels, which create difficulties with regard to the economical use of available vessels and barges.
2. Because of the high kinetic energy of the slurry, part of the useful particulate material from the slurry fails to deposit and is carried back to the river. This results in a longer loading time of the vessel, i.e. a higher energy consumption per unit of useful material. Additionally, it is frequently impossible to load the vessel fully, so that besides the useful sand and/or gravel material, the vessels also contain appreciable amounts of useless water.
3. The useful particulate material deposited from the slurry also contains, in most cases, mud and other harmful components, and it is therefore necessary that it be washed before use in building projects, and this causes an appreciable increase in costs.
4. The water which carries the particulate material to the bank for embanking or for final use spreads the particulate material over a large area, so that considerable mechanization must be used. If the slurry were concentrated before leaving the suction pipe, i.e. if the water were separated from it, the need for such mechanization would be decreased considerably.
The object of this invention is a device by means of which the above shortcomings are removed.
The device of the present invention can also be used for separating other types of granulated material from a fluid flow and for the rough calibration thereof.
The device of the invention functions in such a way that the useful components (sand or gravel) are separated in a moist state or with a negligible percentage of water at one outlet from the continuously fed slurry and the useful particulate components are simultaneously washed. At another outlet, a continuous separation of the water which has served as the transportation medium of the particulate components is simultaneously carried out.